When organic waste present in a landfill decomposes, combustible gas is generated. This gas often has an unpleasant smell and typically includes methane, carbon dioxide, and other constituents, such as hydrogen sulfide and complex hydrocarbons. Landfill gas may cause severe odor problems.
Once landfills have reached full capacity, they are generally capped with among other things, a layer of topsoil to support vegetation and help prevent erosion. A gas vent is sometimes provided to enable the landfill gas generated by the decomposition process to pass through the cap for release.
The gas emerging from the vent may be burned to eliminate the unpleasant odor. A flare is typically provided to burn the gas as it emerges from the vent. While passive flares can be cost effective they routinely burn out. Several factors contribute to this difficulty, including variations in the flow rate of the gas, variations in the percentages of the constituents of the landfill gas, and variations in the gas/air ratio mixture required to maintain a continuous flame. Adverse weather conditions such as wind and precipitation may also extinguish the flame.
Because such passive flares are positioned proximate to the landfill vents to minimize the use of lengthy gas pipe runs, the flares are usually located in remote locations where it is difficult to monitor the presence of a flame. It is very inconvenient to manually re-ignite the flares when the flame is extinguished. During any time in which the flame is out, the gas is permitted to escape into the atmosphere, creating potentially lengthy periods in which the odor is not being treated.
Construction and demolition (C&D) landfills typically do not produce a lot of combustible gas because they do not contain as much organic content compared to Class 3 and Class 1 facilities that typically receive large quantities of organic waste. This means C&D landfills have relatively low gas combustible flow rates through their gas vents. Such a flow rate may be 0.5 CFM to 70 CFM (CFM=cubic feet per minute).
Because conventional gas flares are designed for landfills that contain large amounts of organic waste, they do not burn continuously in low gas flow conditions present at C&D landfills. At C&D landfills, conventional gas flares extinguish routinely because of low combustible gas flow.
In particular, conventional open air/open top/perforated flares are highly susceptible to wind and precipitation. Typical open top/open air/perforated flare allow for the dilution, disruption and dispersion of the landfill gas, preventing consistent combustion. They also allow the wind to direct the gas away from the ignition source. Such problems commonly occur when low combustible gas flow rates exist, which is a common condition at C&D landfills.